Tag Archives: maternal urinary fluoride

Maternal urinary fluoride/IQ study – an update

Model of a fetus in the womb. Photo credit: CP PHOTO/ Alliance Atlantis/ HO) 

The maternal urinary fluoride/IQ study  (Bashash et al., 2017) continues to get attention – but mainly from anti-fluoride organisations. The scientific community will evaluate the published report after giving it due consideration and there have already been criticisms. But anti-fluoride campaigners consider it the best thing since sliced bread. The Fluoride Action Network (FAN) describes it as “a cannon shot across the bow of the 80 year old practice of artificial fluoridation” and Fluoride Free NZ insist that it “must spell an end to fluoridation in New Zealand.”

We expect confirmation bias from the anti-fluoride organisations. But the misrepresentations in the propaganda from these organisations are of more concern because they are blatantly meant to scaremonger.

Misrepresentation by anti-fluoride organisations

These people have worked hard to stress the respectability of the authors of the Bashash et al., (2017) paper and claim the study is impeccable. They are not interested in a critical analysis of the data and the conclusions. And they are completely silent about the evidence from the study showing no association of children’s urinary fluoride levels and IQ – normally they are quick to criticise authors reporting such a lack of association.

But this time as well as their normal misrepresentations they have actually manipulated a figure from the paper. I wonder what copyright law would say about this.

I provided the relevant figures from the paper my earlier article (see   Fluoride, pregnancy and the IQ of offspring) and commented on the large amount of scatter in the data.  This scatter should be a warning to any sensible reader – so FAN simply overcomes that problem by deleting the data points in their presentation of the figure.

Here is the original Figure 2 and the FAN misrepresentation of it:

Notice 2 things:

  1. The original figure showed the data for GCI – general cognitive index. It is not IQ and not presented as IQ in the original paper. But it is a measure  of “verbal, perceptual performance, quantitative, memory, and motor abilities of preschool-aged children.” Perhaps a fine point and FAN may be excused for inserting the more popularly understood term IQ. Or perhaps they decided not to use the real figure for IQ (Figure 3A) because it implied no effect at normal urinary fluoride levels (see figure 3A in Fluoride, pregnancy and the IQ of offspring);
  2. FAN removed all the data points in their presentation of the figure. I am sure FAN would argue this was to “simplify” the figure. But in doing so they have removed what is the most important information in Figure 2 – the wide scatter of the data points. That scatter suggests that even though the reported association is “statistically significant” it explains very little of the observed variation and is therefore not important (and may not even be real).

Association of maternal urinary F with child IQ poor and probably misleading

In Fluoride, pregnancy and the IQ of offspring I estimated that “the reported relationships with maternal urinary fluoride could explain no more than a few percent of the variation in the data.” Purely an estimation because I did not have the data to analyse myself and the authors did not give the relevant statistical information.

I have since used a plot digitiser programme to extract the data for these figures and performed my own statistical analysis.

These are the results:

For Figure 2:

Yes, a “statistically significant” relationship (p = 0.002) but it explains only 3.3% of the variation in GCI (R-squared = 0.033)

For Figure 3A:

Again, “statistically significant” (p = 0.006) but explaining only 3.6% of the variation in IQ (R-squared = 0.0357).

So my estimate was pretty good. And my evaluation is valid:

“In this case, I would expect that other risk-modifying factors that explain the variation more completely could be found. And if these were included in the multiple regressions there may not be any observable relationship with urinary fluoride.”

Considering that this work was unable to explain about 97% of the variation in CGI and IQ I really question its publication. Certainly, scientific evaluations will conclude that this paper should not have any influence on policymakers.

It’s a pity that with all the data the authors had they did not seek out, or properly evaluate, other possible risk-modifying factors.

Other work by group showing no association ignored

Strangely, the Bashash et al., (2017) paper did not include relevant IQ information from the PhD thesis of one of their team Deena B. Thomas. This is her thesis citation:

Thomas, D. B. (2014). Fluoride exposure during pregnancy and its effects on childhood neurobehavior: a study among mother-child pairs from Mexico City, Mexico. PhD thesis, University of Michigan.

It can be downloaded from the full-text link.

The data in chapter 2 of this thesis – Urinary and Plasma Fluoride Levels During Pregnancy and Determinants of Exposure Among Pregnant Women from Mexico City, Mexico – was published. The citation is:

Thomas, D. B., Basu, N., Martinez-Mier, E. A., Sánchez, B. N., Zhang, Z., Liu, Y., … Téllez-Rojo, M. M. (2016). Urinary and plasma fluoride levels in pregnant women from Mexico City. Environmental Research, 150, 489–495.

Bashash et al., (2017) did reference this paper – after all, it dealt with the data they used for estimating fluoride exposure. But they did not reference the thesis itself – and two other chapters in that thesis are directly relevant to the relationship of fluoride exposure to child IQ.

Chapter 3 – Prenatal fluoride exposure and neurobehavior: a prospective study – is directly relevant except that where Bashash et al., (2017) reported data for the children when 4 years old and 6-12 years old Thomas reported data for child neurobehavioral outcomes at ages 1, 2 and 3.

She concluded:

“that maternal intake of fluoride during pregnancy does not have a strong impact on offspring cognitive development in the first three years of life.”

OK – perhaps the difference is purely due to age. But surely it is part of the picture and should at least been mention in the Bashash et al., (2017) discussion.

Chapter 4 – Concurrent Fluoride and Total WASI in 6-15 year old children from Mexico City, Mexico – is also directly relevant because Bashash et al., (2017) did include that data in their paper. They concluded that:

“there was not a clear, statistically significant association between contemporaneous children’s urinary fluoride (CUFsg) and IQ either unadjusted
or adjusting for MUFcr.”

This differs a little from the findings in Thomas’s thesis:

“In the overall population, urinary fluoride appears to have no significant impact on total WASI scores (β =1.32, p=0.33), but this association changes once the models are separated by male and female children. Male children showed a significantly positive trend (β=3.81, p=0.05), and females showing a negative trend that was not significant (β= -1.57, p=0.39).” [WASI score is a measure of IQ]

And she wrote:

“analysis suggests concurrent urinary fluoride exposure has a strong positive impact on cognitive development among males aged 6-15 years.”

She concludes:

“These results were surprising in that they show opposite trends to what has been reported in the literature so, more studies with similar reliable methodology, which account for plasma fluoride, diurnal variations in urinary fluoride and children’s SES, are needed. If these results are substantiated, different fluoride interventions may be needed for male children versus female

I would have thought these findings and conclusions were worthy of discussion by Bashash et al., (2017). It’s not as if the authors were unaware of their colleague’s findings.

Maybe internal politics are involved. but that does not justify the omission.


The anti-fluoride people, and particularly FAN, are misrepresenting the study and have manipulated a figure to hide information in an unethical way. The data presented in the Bashash et al., (2017) study shows maternal urinary fluoride can only explain 3 – 4 % of the variation in General Cognitive Index and IQ of the children. The inclusion of a more viable risk-modifying factor would probably remove even that small amount explanation.  Bashash et al., (2017) also neglected to discuss relevant information from a colleague which contradicted their conclusions.

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Fluoride, pregnancy and the IQ of offspring

Anti-fluoride campaigners don’t agree. Image credit:Dental Care Tips for Mom and Baby” presentation

What’s the story about this new IQ-fluoride study? The one that claims fluoride intake by pregnant women could endanger their children’s IQ?

Whatever the truth, it has certainly got the anti-fluoride activists going. Mary O’Brien Byrne, leader of the local anti-fluoride group is even suggesting people check if their mothers lived in fluoridated areas. And they are busy promoting the newspaper articles on this. For example Fluoride exposure in utero linked to lower IQ in kids, study saysChildren’s IQ could be lowered by mothers drinking tap water while pregnant, and Higher levels of fluoride in urine linked to lower IQ scores in children.

Best not rely on those media reports, though – you know how unreliable they can be. The original paper is available – this is the citation:

Bashash, M., Thomas, D., Hu, H., Martinez-mier, E. A., Sanchez, B. N., Basu, N., … Hernández-avila, M. (2016). Prenatal Fluoride Exposure and Cognitive Outcomes in Children at 4 and 6 – 12 Years of Age in Mexico. Environmental Health Perspectives, 1, 1–12.

And here is a link to the full text. Download it and see what sense you make of it. I warn you it is a difficult paper to read.  A lot of information is lacking and the information that is included is hard to find. The statistical analysis is incomplete.

A new twist on the tired old fluoride/IQ story

Basically, it is the old drinking water fluoride causes lowering of IQ story. This time it relates to a supposed association of fluoride intake by pregnant mothers with cognitive deficits in their children. Interesting, only one other similar study (involving fluoride exposure while pregnant) has been reported – in January this year, and also in Mexico. I wrote about that study of Valdez Jiménez et al., (2017), In utero exposure to fluoride and cognitive development delay in infants,  in the article Premature births a factor in cognitive deficits observed in areas of endemic fluorosis?

Briefly, the Valdez Jiménez et al., (2017) study was from Mexican areas of endemic fluorosis with very high fluoride concentrations in drinking water so the results are not applicable to areas where community water fluoridation is used. However, the high incidence of premature births, and low birthweights for the children, for mothers with high urinary fluoride levels does suggest that problems of birth in areas of endemic fluorosis could provide a biological mechanism to explain the IQ deficits. Rather than a direct chemical toxicity mechanism.

What about the Bashash, et al. (2017) paper?

Generally, the paper concludes that “higher prenatal fluoride exposure . . . .was associated with lower scores on tests of cognitive function in the offspring.”

So here are some concerns I have about the paper

1: An association is not evidence of, or proof for, causation. Yes, that is the normal and obvious qualification for such studies and authors tend to repeat it – even if they might still attempt to argue the case that it is evidence. A lot of confirmation bias goes on with these sort of correlational studies.

2: The information about the mothers is scant. My first question, given it was Mexico, was did they come from areas of endemic fluorosis? The women were recruited from three hospitals in Mexico city but this says nothing about their current or former residential areas. No information on drinking water fluoride is presented nor any biological assessment, such as dental fluorosis, given which could help estimate the role of endemic fluorosis.

3: Assessment of fluoride exposure relied completely on urine fluoride concentration measurements. With between one and three samples for each mother-child pair! (Of the total sampled there was only one sample for 217, two for 224 and three for 71 mothers). I believe that is completely inadequate for estimating exposure – especially as fluoride levels in urine vary markedly during the day and with diet. Besides the extremely low sample numbers,  the World Health Organisation has warned that while urinary fluoride can be useful for monitoring populations “Urinary fluoride excretion is not suitable for predicting fluoride intake for individuals.”  (see Contemporary biological markers of exposure to fluoride). They further warn that 24 hr collection is preferred to the spot sampling used in this study.

4: The statistical information presented is confusing – and insufficient to estimate how relevant the reported statistically significant associations are. I believe the best idea of the data can be gleaned from the following figures presented in the paper.

Figure 2 displays the data and association of maternal urinary fluoride (MUFcr) with a general cognitive index (CGI) for the 4 yr old offspring.

Figure 3A displays the data and association of maternal urinary fluoride (MUFcr) with IQ of the offspring at age 6 -12.

While linear regression analysis showed statistically significant associations of the CGI and IQ of offspring’s with maternal urinary fluoride levels the large scatter indicates these associations will explain only a small part of the variations observed. In such situations, reliance on p values can be misleading. As a reader, I would be more interested in the R2 values which indicate the amount of variation explained by the association.

I estimate the reported relationships with maternal urinary fluoride could explain no more than a few percent of the variation in the data. In this case, I would expect that other risk-modifying factors that explain the variation more completely could be found. And if these were included in the multiple regressions there may not be any observable relationship with urinary fluoride.

I discussed this issue more fully in my article Fluoridation not associated with ADHD – a myth put to rest which showed that a published relationship of ADHD with fluoridation extent disappeared completely when altitude was included as a risk-modifying factor. And that relationship showed less scatter of the data points than in the figures above.

5: The absence of any association of child IQ to child urine fluoride was also reported in this paper. This conflicts with other researchers working in areas of endemic fluorosis who have reported such associations. It could be that the urine fluoride measurements used in the present study were not suitable. But I am picking that the anti-fluoride campaigners will be very silent about that information, given the importance they give to other studies showing a relationship in their propaganda.


it is a very unsatisfying paper. I couldn’t determine if areas of endemic fluorosis were implicated – as they were for the Valdez Jiménez et al., (2017) study. Urinary fluoride is an inadequate measure of fluoride exposure – especially for individuals and spot samples – and its variability does not allow comparison with other studies and other regions. I couldn’t evaluate if the reported results were relevant to New Zealand which does not have any endemic fluorosis.

Finally, I believe aspects of the statistical analysis were inadequate. But on the positive side, I am pleased the authors did display the actual data in their figures. The information in those figures forced me to conclude that maternal urinary fluoride may not have the influence the authors suggest. If it does have an influence its contribution can only be minor and other more important risk-modifying factors will be involved.

Mind you – I am sure anti-fluoride campaigners will see it differently. They are currently heavily promoting the study and anti-fluoride guru Paul Connett sees it as the best thing since sliced bread. He has gone on record to say this means the end of community water fluoridation!


I think the anti-fluoride people are aware of weaknesses in this study. The local Fluyodie Free NZ has put out a press release including a figure which they have doctored to remove the data points which show how little variation is explained. Compare their figure with the Fiugure 2 above.

Fluoride Free NZ doctors figure from paper to hide the scatter in data points showing how little of the variability the relationship explains

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